🚀 go-pugleaf

A co-worker of mine brought up an interesting idea.
He thinks it might be very difficult to intercept data
by tapping a phone line of someone using a modern high
speed full duplex modem.  The reason is that the full
available bandwidth of the phone line is being used
in both directions; the modems separate out the signals
with echo cancellation, which means that the modem
takes the phone signal and subtracts what it itself
is sending--the difference is what the other modem
is sending.  But a wiretapper might have an awfully
hard time of separating the two signals.  

Any thoughts?

Sci.crypt is probably not the right place for this,
but I felt people here might be interested in the idea.